CaMK4 drives podocyte injury

Podocyte dysfunction is a hallmark of kidney injury and occurs in both autoimmune and nonautoimmune renal diseases. Calcium signaling underlies podocyte injury; however, the factors that promote calcium signaling in podocytes in response to injury are not fully understood. In this episode, George Tsokos and colleagues demonstrate that Ca2+/calmodulin–dependent kinase 4 (CaMK4) is increased in podocytes from patients with lupus nephritis and focal segmental glomerulosclerosis and in mouse models of lupus and kidney injury. Moreover, administration of a CaMK4 inhibitor prevented nephritis in lupus-prone mice and ameliorated podocyte damage in mice with kidney injury. Togeither, this study identifies CaMK4 activation as a driver of podocyte dysfunction and suggests CaMK4 inhibition be further explored for treating podocytopathies.

Abstract

Podocyte malfunction occurs in autoimmune and nonautoimmune kidney disease. Calcium signaling is essential for podocyte injury, but the role of Ca2+/calmodulin–dependent kinase (CaMK) signaling in podocytes has not been fully explored. We report that podocytes from patients with lupus nephritis and focal segmental glomerulosclerosis and lupus-prone and lipopolysaccharide- or adriamycin-treated mice display increased expression of CaMK IV (CaMK4), but not CaMK2. Mechanistically, CaMK4 modulated podocyte motility by altering the expression of the GTPases Rac1 and RhoA and suppressed the expression of nephrin, synaptopodin, and actin fibers in podocytes. In addition, it phosphorylated the scaffold protein 14-3-3β, which resulted in the release and degradation of synaptopodin. Targeted delivery of a CaMK4 inhibitor to podocytes preserved their ultrastructure, averted immune complex deposition and crescent formation, and suppressed proteinuria in lupus-prone mice and proteinuria in mice exposed to lipopolysaccharide-induced podocyte injury by preserving nephrin/synaptopodin expression. In animals exposed to adriamycin, podocyte-specific delivery of a CaMK4 inhibitor prevented and reversed podocyte injury and renal disease. We conclude that CaMK4 is pivotal in immune and nonimmune podocyte injury and that its targeted cell-specific inhibition preserves podocyte structure and function and should have therapeutic value in lupus nephritis and podocytopathies, including focal segmental glomerulosclerosis.